Internet Protocol (IP) based telephony systems are often implemented with a centralized architecture. Such systems typically include a call control system deployed at one main office of an enterprise. The call control system may provide call management and voice messaging services from the main office to remote branch offices of the enterprise. This centralized architecture is attractive to many enterprises in that it enables system administrators to easily provision and manage the call control system from the main office. IP-based telephones at the branch offices may be connected with the main office over a wide area network (WAN). Telephone users at the branch offices may remotely access services from the main office call control system over the WAN, such as retrieving voice messages stored by the call control system.
Unfortunately, such configurations can be seriously impacted by WAN communication interruptions. For example, in the event of a WAN outage, IP-based phones at the branch offices will be unable to access services of the main office. In particular, voice messages stored by the call control system of the main office will be unavailable to users at the branch offices. This can detrimentally affect the business and customer response times of the branch office users.
One approach to handling such problems uses a decentralized telephony system architecture with multiple complete call control systems. In this case, a complete call control system with call management and voice messaging services may be located at each branch office. The individual call control systems are independently operated and therefore are not subject to service interruptions due to WAN failures between the main office and branch offices.
However, such an approach fails to provide the implementation flexibility offered by a centralized architecture. For example, when a remote user relocates to a different branch office, the user's voice mailbox cannot be seamlessly moved between the different call control systems of the branch offices. In addition, this decentralized approach fails to provide the scalability offered by a centralized architecture. Indeed, the cost and time associated with managing of multiple complete call control systems at every branch office can be cost prohibitive for many enterprises.
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